1. Technical Field
Anti-reflective coating polymers used in a photolithography process, which is one of the fabrication processes for a semiconductor device are disclosed. A method for preparing the anti-reflective coating polymer, and an anti-reflective coating composition comprising the anti-reflective coating polymer are also disclosed. The disclosed anti-reflective coating polymers can be used in immersion lithography for the fabrication of sub-50 nm semiconductor devices.
2. Description of the Related Art
A photolithography process is a process for the transfer of a semiconductor circuit pattern formed on a photomask to a wafer. Photolithography is one of the most important steps in determining the fineness or side and integration density of circuits in the fabrication of semiconductor devices.
In recent years, as the integration density of semiconductor devices has increased, new techniques have been developed that are adapted to fine processing required in the fabrication of semiconductor devices. Under these circumstances, there is an increasing need for an ultrafine photolithography process technique. That is, as the circuit linewidths become finer and finer, the use of short-wavelength light sources for illumination, such as KrF, ArF, F2 and EUV excimer lasers, and high numerical aperture lenses is required. EUV, F2, ArF and KrF lasers in this order are preferentially used as light sources because of their short wavelength.
A number of studies on the development of sub-50 nm devices have been actively undertaken. In response to these studies, recent attention has been directed toward the development of suitable processing equipment and materials associated with the use of F2 and EUV as exposure light sources. Technical solutions for the use of F2 are satisfactory to some extent, but there are the following problems: 1) the mass production of high-quality CaF2 within a short time is limited, 2) since soft pellicles are likely to be deformed upon exposure to light at 157 nm, the storage stability is decreased, and 3) hard pellicles incur considerable production cost, and are difficult to produce on a commercial scale due to their nature of light refraction.
On the other hand, since suitable light sources, exposure equipment and masks are required to use an EUV laser, it is not yet suitable for practical use. Accordingly, the formation of finer high-precision photoresist patterns by using a photoresist adapted to the use of an ArF excimer laser has now become a key technical task. Under these circumstances, immersion lithography has recently drawn significant attention.
Dry lithography is a currently used lithography process, and is an exposure system wherein air is filled between an exposure lens and a wafer. In contrast to dry lithography, immersion lithography, which corresponds to a NA (numerical aperture) scaling technique, is an exposure system wherein water is filled between an exposure lens and a wafer. Since water (refractive index (n)=1.4) is used as a medium for a light source in the immersion lithography, the NA is 1.4 times larger than that in the dry lithography using air (refractive index (n)=1.0). Accordingly, immersion lithography is advantageous in terms of a higher resolution.
A problem encountered with the fabrication of a sub-50 nm semiconductor device is that an alteration in the critical dimension (CD) of a photoresist pattern inevitably takes place, during the process for the formation of an ultrafine pattern, by standing waves, reflective notching, and diffracted and reflected light from an underlayer due to the optical properties of the, underlayer on an overlying photoresist and due variations in the thickness of the photoresist. To prevent reflected light from the underlayer, a light-absorbing material, called an “anti-reflective coating,” at a wavelength band of light used as an exposure light source is introduced between the underlayer and the photoresist. A bottom anti-reflective coating interposed between the underlayer and the photoresist has been used. With the recent increase in the fineness of overlying photoresist patterns, a top anti-reflective coating (TARC) has also been used to prevent the photoresist pattern from being disrupted by the reflected and diffracted light. Specifically, as the remarkable miniaturization of semiconductor devices makes overlying photoresist patterns extremely fine, the use of a bottom anti-reflective coating alone cannot completely prevent the patterns from being disrupted by scattered reflection. Accordingly, a top anti-reflective coating is used to prevent the disruption of the patterns.
However, since conventional top anti-reflective coatings for use in dry lithography are water-soluble (in the case of using KrF or ArF laser), they cannot be applied to immersion lithography. In other words, since water is used as a medium for a light source in immersion lithography, the conventional top anti-reflective coatings are easily dissolved in the water.
Accordingly, an ideal top anti-reflective coating for use in immersion lithography must satisfy the following requirements:
first, the top anti-reflective coating must be transparent to a light source;
second, the top anti-reflective coating must have a refractive index between 1.4 and 2.0, depending on the kind of an underlying photosensitive film (i.e. photoresist) to be used;
third, when the top anti-reflective coating composition is coated on an underlying photosensitive film, it must not dissolve the photosensitive film; f
fourth, the top anti-reflective coating must not be soluble in water upon light exposure; and
finally, the top anti-reflective coating must be soluble in a developing solution upon development.
The above-mentioned stringent requirements make the development of a suitable top anti-reflective coating for use in immersion lithography extremely difficult and challenging.
Thus, there exists a strong need for the development of a top anti-reflective. coating for use in immersion lithography which is water-insoluble and can minimize the alteration of CD.